Metabolite Fruit Profile Is Altered in Response to Source-Sink Imbalance and Can Be Used as an Early Predictor of Fruit Quality in Nectarine

Tissue-specific transcriptional analysis outlines calcium-induced core metabolic changes in sweet cherry fruit

The role of calcium in fruit ripening has been established, however knowledge regarding the molecular analysis at fruit tissue-level is still lacking. To address this, we examined the impact of foliar-applied calcium (0.5% CaCl₂) in the ripening metabolism in skin and flesh tissues of the sweet cherry 'Tragana Edessis' fruit at the harvest stage. Exogenously applied calcium increased endogenous calcium level in flesh tissue and reduced fruit respiration rate and cracking traits. Fruit metabolomic along with transcriptomic analysis unraveled common and tissue-specific metabolic pathways associated with calcium feeding. Treatment with calcium diminished several alcohols (arabitol, sorbitol), sugars (fructose, maltose), acids (glyceric acid, threonic acid) and increased ribose and proline in both fruit tissues. Moreover, numerous primary metabolites, such as proline and galacturonic acid, were differentially accumulated in calcium-exposed tissues. Calcium-affected genes that involved in ubiquitin/ubl conjugation and cell wall biogenesis/degradation were differentially expressed between skin and flesh samples. Notably, skin and flesh tissues shared common calcium-responsive genes and exhibited substantial similarity in their expression patterns. In both tissues, calcium activated gene expression, most strongly those involved in plant-pathogen interaction, plant hormone signaling and MAPK signaling pathway, thus affecting related metabolic processes. By contrast, calcium depressed the expression of genes related to TCA cycle, oxidative phosphorylation, and starch/sucrose metabolism in both tissues. This work established both calcium-driven common and specialized metabolic suites in skin and flesh cherry tissues, demonstrating the utility of this approach to characterize fundamental aspects of calcium in fruit physiology.

Amino Acid Profiles in Peach (Prunus persica L.) Fruit

Amino acids play an interesting and important role in the metabolism of peaches. The objectives of this study were to investigate and compare amino acid profiles in peaches at harvest for future research about the resistance effects, nutritional value of amino acids in peaches and to produce high-quality peach wine. In the study, 10 peaches and nectarines, including white, yellow and red flesh varieties, were selected for amino acid concentration and composition by high performance liquid chromatography (HPLC). Results showed sugar levels in nectarines were higher than in peaches in this study. High concentrations of total acids were found in “Tropic Prince”, “Yixianhong”, “NJN76” and “Hongrou1”. Malic acids had the highest concentrations, compared toquinic and citric acid concentrations. Total amino acids in yellow and white flesh varieties were over 1100 µg/g FW, while red flesh varieties had total amino acids below 750 µg/g FW. Asn was the highest concentration compared to other amino acids, with the high concentration of Asn in “Tropical Prince’ (3279.15 µg/g FW) and the lowest concentration in “Touxinhong” (559.60 µg/g FW). “Jinxia”, “Yuhua3” and “Chengxiang” had better amino acid scores compared with others, in particularly the lowest value in the red flesh varieties. Finally, according to PCA and the heatmaps, amino acids in “Chengxiang”had evident differences to other varieties, which showed the different amino acid concentrations and composition. Overall, the results of this study highlighted three yellow flesh and one white flesh varieties that had satisfactory concentrations and components of amino acid values. In addition, amino acids were the precursors of aroma compounds, so these differences between varieties werea new way to screen the potential varieties for producing high quality peach wines with the anticipated specific characteristics.

Identifying sources of metabolomic diversity and reconfiguration in peach fruit: taking notes for quality fruit improvement

The metabolomic content determines many of the important features of a fruit, such as its taste, flavor, color, nutritional value, and abiotic or biotic resistance. Peach (Prunus persica (L.) Batsch) is one of the best genetically characterized species used as a model for Rosaceae, the drupes of which are a source of minerals, vitamins, fiber, and antioxidant compounds for healthy diets around the world. During the last few years, a great advance in the analysis of the metabolic diversity and reconfiguration in different peach varieties in response to developmental and environmental factors has occurred. These studies have shown that the great phenotypic diversity among different peach varieties is correlated with differential metabolomic content. Besides, the fruit metabolome of each peach variety is not static; on the contrary, it is drastically configured in response to both developmental and environmental signals, and moreover, it was found that these metabolic reconfigurations are also variety dependent. In the present review, the main sources of metabolic diversity and conditions that induce modifications in the peach fruit metabolome are summarized. It is postulated that comparison of the metabolic reconfigurations that take place among the fruits from different varieties may help us better understand peach fruit metabolism and their key drivers, which in turn may aid in the future design of high‐quality peach fruits.